Hygroscopic coil for humidity indicators



Sp. 6, F'JI P. o. UNSER HYGROSCOPIC COIL FOR HUMIDITY INDICATORS FiledFeb. 14, 1947 Patented Sept. 6, 1949 UNITED STATES HYGRUSCOPIC COIL FOR,HUMIDITY INDICATORS Paul 0. Unger, Elmhurst, Ill., assignor to AutopointCompany, Chicago, Ill., a corporation of Illinois 9 claims. l

The present invention relates to a humidity indicating mechanism crdevice for indicating the relative humidity in a room or other enclosureand more particularly to -a novel hygroscopic coil or element for use insuch indicating mechanism.

The recording or indicating of the relative humidity by a suitableinstrument embodying a member formed of a strip of hygroscopic materialattached to a strip or backing of thin metal or the like and in whichchanges in the physical dimensions are indicative of the relativehumidity have been employed. However, in such prior devices thehygroscopic material has been either aflixed to the metal .backing by anadhesive, or the longitudinal edges of the metal or backing have beenbent or flanged over the edges of the hygroscopic strip.

Both of these prior methods have numerous inherent disadvantages, themost important of which is that the hygroscopic material in such devicesin a relatively short time become loose or partially detached and unlessthey remain permanently united to the metal strip or tape longitudinallyand transversely thereof, variations in the longitudinal dimensions ofthe hygroscopic or control material is not accurately transmitted to themetal strip and from it to the indicating means.

Joining the hygroscopic material or element to the metal backing by glueor other suitable adhesive, has the serious drawback that weatherconditi-ons aiiect the adhesive and thus the property of the absorbentor hygroscopic material to absorb moisture varies from day to day. Asthis adhesive dries out or loses its adhesive properties, the absorbentmaterial becomes loose or detached and naturally its dimensionalvariations are not directly related or transmitted tto the metal backingor tape for accurately indicating the relative humidity.

Attempts have been made to obviate the above condition by joining thehygroscopic or absorbent strip to the metal strip or .backing by bendingor anging over the longitudinal edges of the backing strip onto theadjacent edges of the hygroscopic material. However, such method hasbeen unsuccessful for the reason the hygroscopic material soon worksloose or bows transversely.

Both of these methods have the further disadvantage that the undersideof the hygroscopic material or strip, i. e. the side adjacent the metalstrip, is not exposed to the humidity to be measured or determined.

The present novel embodiment of hygroscopic coil comprises a strip ofhygroscopic or absorbent material permanently secured to a thin metallicstrip or backing in such manner that they continuously function as aunit and any longitudinal extension or variation in the physicaldimensions of the hygroscopic material is accurately transmitted to thethin metallic strip and from it to a suitable indicating means.

Another important object of the present invention is the novel means andmanner of joining the hygroscopic strip and thin metal .backing wherebyboth sides of the absorbent strip are exposed to the humidity to bedetermined and thereby assure maximum effectiveness. In the noveldisclosed embodiment this is accomplished by longitudinally sewing orstitching these members together in such manner as to prevent theirbecoming loose or detached either longitudinally or transversely.

succinctly stated, among the advantages of the present invention oversuch prior hygroscopic coils are as follows:

(l) There is no adhesive that will cau-se variation in the Aabsorptiveproperties or characteristics of the hygroscopic or absorbent material.

(2) The edges remain exposed and not covered or hanged over.

(3) The hygroscopic or absorbent material cannot work loose or bowlongitudinally or transversely.

(4) By sewing or stitching the hygroscopic material to the thin strip ortape of metal, perforations are made in the metal which expose theunderside of the absorbent material.

(5) The threads used in stitching or sewing have a wicking action whichaugments the absorptive capacity of the hygroscopic coil.

Further objects are to provide a construction of maxi-mum simplicity,eiciency, economy and ease of assembly and operation, and such furtherobjects, advantages and capabilities as will later more fully appear andare inherently possessed thereby.

The invention further resides in the construction, combination andarrangement ci parts illustrated in the accompanying drawing, and whilethere is shown the-rein a preferred embodiment, it is to be understoodthat the same is susceptible of modication and change. and comprehendsother details, arrangements of parts, features and constructions withoutdeparting from the spirit of the invention.

In the drawing- Figure 1 is a perspective View of an assembled humidityindicator employing the novel hygroscopic coil.

Fig. 2 is a View in perspective of the hygroscopic coil and assembledparts removed from the humidity indicator.

Fig. 3 is a fragmentary view in perspective of the composite strip ofhydi'oscopic material and a metallbacking'and ybefore this compositestrip is bent into=the form of a coil.

Fig. 4 is a View in Vertical cross-section taken in a plane repre-sentedby the line 4-4 of Fig.'3.

Referring more particularly .to the disclosure in the drawing and thenovel embodiment therein shown, Fig. 1 shows one form of humidityindicating device i in which ythe present hyg10- scopic coil is mountedand indicates or records the relative humidity in the room or enclosurein which the device is placedor located. As therein shown, the deviceincludes a housing 2 having an opening 3 preferably enclosed --by atransparency, and a stationary scale l divided :to sprovide fspacedindications 5 and 6, the -uppeiwones 5 vdesignating the lrelativehumidity in the 'room or Ienclosuredetermined by a movable indicator orpointer while the lower ones 5 mayfginclude indications lor designatingthe room temperature by means oi a vmovable vindicator or pointer 8.

`The .novel hygroscopicfcoil 9 for indicating the #relative humidity inthe yroorn or enclosure is .shown as 'having'its one end -i suitablysecured y'to and nretained stationary by a bracket or support r'H:mounted in-theinterior of the housing .-2. The .other yend :i2 -issecured vto a rotatable .shaft i3 `which in turn vis connected to an arm-ifiifcar1iying the movable .indicator or pointer l.

The coil :Sl is formed as A:more clearly shown in Figs. 3 :and 4, and'comprises acoextensive strip :i:

i5 of hygroscopic absorbent material and a thin rnc-tal backing or tapeyit. 'This tape or baci;- ng -is of fa resilient `for 'yieldable metalresistant to corrosion. Such a metal maybe a thin strip lof brassor thelike having sufficient inherent re- `s siliency or flexibility to :coilor uncoil Iin accord- .ance with the lelongation or change Yin the-dimensions of the hygroscopic material ydue to the moisture content orhumidity kof the atmosphere f'in :theroom or lenclosure in which thehumidity L;

indicator is located.

In order that the elongation or change in dismensions :of .thehygroscopic stripI i5 is accurately .and 4promptly transmitted to themetal backingstrip li6 and from it to the arm it and the indicator Fl,and -to prevent the strip I5 from becoming detached from the metal'backing strip i6, these strips are securely vjoined by relativelyclosely spaced rows of stitching or sewing l'i' ,and with each rowpreferably extending lonigitud-inally of the composite strip. Thissewring-orstitching produces .-a permanent union between these stripsand with the thread piercing Vvthe `thin metal backing i6 closely spacedopenings are provided in the latter which permit the .moisture to enterand be transmitted to the underside of the hygroscopic strip l5. As theedges Aof this strip are also exposed to the moisture, it will beapparent that an accurate indication of the moisture content andrelative humidity in the room may be had.

As the thread employed in sewing or stitching the strips together toform a composite and permanently joined element'is of cotton or othermaterial having a wicking action, the moisture absorptive capacity ofthe hygroscopic coil is enhanced. The material employed for thehygroscopic element l5 maybe absorbent paper, wood pulp or othersubstance having .the necessary .absorption properties randcharacteristics.

After the composite strip is formed in the manner shown in Figs. 3 and4, it is bent into the form of a coil as shown in Fig, 2, with the endIii anchored upon the stationary bracket or support Il, and -the other`end vIZ anchored in the slotted end of the rotatable shaft 13, wherebyany elongation or change in dimensions of the hygroscopic strip I5 ispromptly transmitted to the thin metal backing I6, and such elongation.causes the coil to wind or unwind in accordance with the moistureabsorbed. Thus the relative vhumidity is directly transmitted to the armI4 ,and the yindicator or pointer 'l which registers such relativehumidity on the indications 5 on the scale 4.

Having thus disclosed the invention, I claim:

l. A'hygroscopic coil for a humidity indicator, comprising acompositeelement including a thin metal-backing, Ia strip of :absorbentmaterial vand absorbent threads piercing the absorbent dmateriaiandmetal bach-ing whereby :they are permanently joined together.

2. In Va hygroscopic coil for humidity indicators, a laminated membercomposed of a -`,thin strip of flexible metal, ya strip of-hygroseopicmaterial and spaced 'rows of threads joining and permanentlyconnecting the hygroscopic material to the metal.

3. A hygroscopic-coil for 'indicating the relative humidity in a roomlor -other enclosure, comprising a member formed of a relatively thinstrip vvof vflexible metal, athin strip Aof absorbent :materialcoextensive therewith, -and'spaced-rows of threads Vextending throughand j oining said'strips together to vform a permanently joinedcomposite member.

4. A hygroscopic coil for a humidity indicator, comprising coextensivestrips of an-absorben't material and a thin exible fmetal, andlongitudinal rows of absorbed threads extending through the metal stripfor permanently joining the strips.

5. A hygroscopic-coil for indicatingthe'relative humidity in a room orother enclosure, comprising a composite member formed into a :coil andincluding a backing-of thin exible metal and astrip of hygroscopicmaterial coextensive'with the backing, and threads extending through andpermanently joining said metal and hygroscopic material whereby toprevent detachment or loosening thereof -due to elongation or change indimensions-of thehygroscopic material by reason or changes in themoisture content in the `enclosure.

6. A hygroscopic coil for indicating the relative humidity in a room orother enclosurepcomprising a composite member formed into a coil andincluding a ybacking of thin flexible metal .and .a strip of hygroscopicmaterial coeXtensive with the backing, and spaced rows vof threadsstitching and joining the metal backing 'and hyg-roscopic material Yintova permanently joined, composite structure.

7. A hygroscopic-coil 4for a humidity indicator, coniprisingcoextensivestrips of an absorbent material and a thin vflexible metal, andlongitudinal rows of threads sewn through the ilexible metal .to thereatprovide openings 'for exposing lthe underside of the hygroscopicmaterial to the `moisture content.

`8. In a hygrosoopic coil for humidity indicators, a laminated membercomposed of a 'thin strip of flexible metal Vand a strip of hygroscopicmaterial, .and longitudinal rows or threads or an absorbent material forjoining `the strips to form a composite structure, said threadsextending .through :the flexible metail and having -a wicking action fortransmitting moisture to the hygro- REFERENCES CITED scopic material.

9. The method of forming a hygroscopic coil for humidity indicators,comprising the steps of providing coextensive lengths of a thin flexiblemetal backing and a hygroscopic material, sew- The following referencesare of record in the le of this patent:

UNITED STATES PATENTS ing the coextensive lengths together with theHugelgz Tengglle Sepj'gelg., threads extending therethrough topermanently 772027 Buttere Oct '11 190; unite these lengths into acomposite member, and 912815 Cook Feb' 16 1909 forming the compositemember into a coil. in 1 9562795 Henning"" Max; l 1934 2,016,973Pistilli Oct. 8, 1935 PAUL 0 UNGER' 2,093,767 Roiiefson sept, 21, 1937

